well i don't know..i think kyoraku,ukitake and yamamoto will have the coolest and stongest bankais as tite kubo still hasn't showed us their bankai and he mention that these 3 are the strongest captains...you may argue that hitsugaya is the strongest or kenpachi or byakuya but kubo said these are the top so..besides we haven't even seen them fight..i imagine it's gonna be awesome